Climate scientists have estimated that, in order to avoid runaway global warming, the world would need to cut its carbon emissions roughly in half by 2050. Since emissions in developing countries like China and India are still rising fast , meeting this target would require developed nations to aim for a figure more like 80 percent. When you consider that the United States, the largest polluter in the developed world, has no real strategy in place to achieve that — and that no binding international agreements appear to be on the horizon — the goal can start to sound nigh impossible. The task is so intimidating that even serious people are starting to entertain extreme-sounding geoengineering ideas like flying business jets into the stratosphere and spraying sulfuric acid all over the place to try to deflect sunlight before it reaches the Earth. Others reckon it’s already t...